A torsion damper of the above kind is described in the specification of U.S. Pat. No. 4,613,029, which proposes to provide third resilient means interposed circumferentially between the damper plate and the hub. These third resilient means are so designed as to enable the teeth of the damper plate to come into positive circumferential abutment with the teeth of the hub, while at the same time producing a noise-suppressing or sound-deadening braking effect. In this way the damper plate teeth are enabled to come gently into engagement with the hub teeth, with noises due to impact between the two sets of teeth thus being avoided. In one embodiment, a ring of resilient material is engaged around one of the teeth of one of the sets of teeth, in a groove on that tooth, and is arranged to be compressed by the neighbouring teeth of the other set.
Such an arrangement is effective when the equipment is new, but is liable to deteriorate over a period of time. In addition, the teeth which receive these damping rings (or the damping ring if there is only one) are weakened, and the torque which they can transmit is thus reduced.
In order to overcome the above drawbacks, it has been proposed in the unpublished French patent application No. 90 07866, filed on 22 Jun. 1990 in the name of the same Applicant as French patent application No. 90 14872 on which the present application is based, to make the third resilient means in the form of a ring of resilient material which extends parallel to the damper plate and which is provided with a set of teeth complementary to those on the hub. These complementary teeth mesh with the hub teeth, defining between them a further circumferential clearance which is smaller than the circumferential clearance that is provided between the damper plate teeth and the hub teeth. The set of teeth on the hub is extended axially so that it can mesh with those of the damper plate and the said ring (the latter being referred to as a shock absorbing ring herein).
The shock absorbing ring is arranged to rotate with the damper plate, and is of resiliently deformable material at its inner periphery. In certain applications, with a view to simplifying manufacture, and also with a view to obtaining satisfactory durability, it may be desirable that this shock absorbing ring is made rigid at its inner periphery.